In fact she had done nothing wrong at all but her younger brother Tomo peed in his pants in his school(in class?).
Asami was very upset and she required him to recieve a punishment,but Natsuo asked Asami to punish her instead of Tom.
Then Asami agreed to punish Natsuo,so Natsuo was spanked by Asami with a ruler.

She tried to refuse to pull down her panties first,but then she resigned herself to a bare bottom spanking.